Scale Calibration

So - I got all scared last night (since I am all alone in the big house and I have a wild imagination) and ended up staying up until 1ish in the morning trying to figure out my stupid scale and how it works.
I put free weights on it in an attempt to calibrate it - everything from 7.5lbs (the lowest it would register) to 50lbs. I did this all with 2.5lb and 5lb weights - so it was a great deal of effort and thought put into all of this with equations and charts and tables (since I am a nerdy engineer I was actually really excited to be doing this all). I made a calibration chart with all the actual weights and scale readings and fit a line to that curve and tried all different forms of the line - linear, exponential, power, modal, etc. and none of them fit perfectly although the linear was the closest (of course since it was not only the first one I tried but also the simplest). I got the equation (I told excel to tell me it though it's not hard to figure it out) and did some math, which seemed off to me so I checked the R^2 value to check how well the line fit the curve and it was 0.997 or something which is excellent but still I didn't think the math was really right. I went to the Doctor's in August and I was a couple pounds over (X)lbs then (however the scale could have gone down a teensy bit more so I though (X) even would have been a better weight). I got on this new scale (the one I am having trouble with) late October and it said (X-1).something then. If my calibration curve is accurate then the weight of (X-5).4lbs (what I was told by my scale yesterday) would actually be close to (X-13)lbs which doesn't seem right to me since I don't think I have lost that much weight. If the scale has always been this wonky (which I don't think it has) then the original weight of (X-1).something would be significantly less and that would be near impossible since I was eating utter crap between my doctor's appointment and when I got on the new scale. UGH! (note: sorry about the confusing X's I am just not ready to state my weight yet)
I also calibrated my other scale (it is a dial one) and that was easy to do since I just placed the weights on it and moved the dial to the right place. I then used a complicated method of trying to calibrate the other one to that one with me but that didn't seem to work.
So all in all, I have no way to know whether or not my scale is accurate or not. I can't go to a gym because my membership to the one at my university is gone (since I have graduated) and all others cost money as well and I don't want a membership - just a chance to weigh myself on the accurate scales. I guess I could go to a doctor's office or something, but I have no insurance right now (no longer covered under my parents and have no benefits at my contract job here) and don't know if that would count as something I need to pay for.
I got on the scale this morning and it said a loss of 6lbs. The dial scale said that I should be around a loss of 8lbs or so (it is hard to tell exactly what number it is on since I am so far from it and leaning over to look at it changes the number). I think I am around a loss of 8lbs and that as the scale gets that high in number the degree of error lessens from when it is lower values such as 50 (which was the absolute highest value I could get on my own). I might try calibrating it some more and experimenting with weights more when I have D around to help me since he can not only lift more than me, but that would be two sets of hand and arms to lift rather than just my one. But for now I am just going to approximate myself on the dial scale and then get on the other one and see for now. I think I am about at a loss of 8lbs and not a loss of 6lbs like it says. I don't know.
Mind you, in all this calibrating I got a really good workout. I was lifting weights for about an hour or so and standing up and sitting down constantly and then leaning over bending, picking up weights while bending. I bet you I worked my arms, back and legs - so I mean, it wasn't a complete waste - haha!